The present invention relates to a magnetic memory element and a magnetic memory device, and particularly to a magnetic memory element having a tunneling magnetoresistive effect and a magnetic memory device using the same.
The magnetoresistive (MR) effect is a phenomenon that the electric resistance is changed by applying a magnetic field to a magnetic substance, and is utilized for a magnetic field sensor, a magnetic head, and the like. Particularly, as giant magnetoresistance (GMR) effect materials exhibiting a very large magnetoresistive effect, artificial lattice films of Fe/Cr, Co/Cu, and the like have been introduced in non-patent documents 1 and 2 (D. H. Mosca et al., “Oscillatory interlayer coupling and giant magnetoresistance in Co/Cu multilayers”, Journal of Magnetism and Magnetic Materials 94 (1991) pp. L1-L5, and S. S. P. Parkin et al., “Oscillatory Magnetic Exchange Coupling through Thin Copper Layers”, Physical Review Letters, vol. 66, No. 16, 22 Apr. 1991, pp. 2152-2155).
There has also been proposed a magnetoresistive effect element using a lamination structure comprised of ferromagnetic layer/non-magnetic layer/ferromagnetic layer/antiferromagnetic layer having a non-magnetic metal layer which is thick to such a degree as to eliminate the exchange coupling action between the ferromagnetic layers. In this element, the ferromagnetic layer and the antiferromagnetic layer are exchange-coupled to each other. Thus, the magnetic moment of the ferromagnetic layer is fixed, so that only the spin of the other ferromagnetic layer can easily be reversed in the external magnetic field. This is an element known as a so-called spin valve film. With this element, the exchange coupling between the two ferromagnetic layers is weak and hence the spin can be reversed in a small magnetic field. For this reason, the spin valve film can provide a magnetoresistive element with a higher sensitivity than that of the exchange coupled film. As the antiferromagnetic substance, FeMn, IrMn, PtMn, or the like is used. The spin valve film causes an electric current to flow in the film in-plane direction for use, but is used for a reproducing head for high density magnetic recording because of such feature as described above.
On the other hand, a non-patent document 3 (W. P. Pratt et al., “Perpendicular Giant Magnetoresistances of Ag/Co Multilayers”, Physical Review Letters, vol. 66, No. 23, 10 Jun. 1991, pp. 3060-3063) shows that the use of the perpendicular magnetoresistive effect of allowing an electric current to flow in the direction perpendicular to the film plane enables to obtain a further larger magnetoresistive effect.
Further, a non-patent document 4 (T. Miyazaki et al., “Giant magnetic tunneling effect in Fe/Al203/Fe junction”, Journal of Magnetism and Magnetic Materials 139 (1995), pp. L231-L234) also shows a tunneling magnetoresistive (TMR) effect due to the ferromagnetic tunnel junction. This tunneling magnetoresistance is obtained by, in a three-layer film comprised of ferromagnetic layer/insulating layer/ferromagnetic layer, causing the spins of the two ferromagnetic layers to be parallel or anti-parallel to each other by the external magnetic field and thereby using a difference in magnitude between the tunnel currents in the direction perpendicular to the film plane.
In recent years, the studies on use of GMR and TMR elements for a nonvolatile magnetic memory semiconductor device (MRAM: magnetic random access memory) have been shown in, for example, non-patent documents 5 to 7 (S. Tehrani et al., “High density submicron magnetoresistive random access memory (invited)”, Journal of Applied Physics, vol. 85, No. 8, 15 Apr. 1999, pp. 5822-5827; S. S. P. Parkin et al., “Exchange-biased magnetic tunnel junctions and application to nonvolatile magnetic random access memory (invited)”, Journal of Applied Physics, vol. 85, No. 8, 15 Apr. 1999, pp. 5828-5833; and ISSCC 2001 Dig of Tech. Papers, p. 122).
In this case, a pseudo-spin valve element in which a non-magnetic metal layer is sandwiched between two ferromagnetic layers different in coercive force, and a ferromagnetic tunneling effect element have been studied. When these elements are used for an MRAM, they are arranged in a matrix form, and an electric current is made to flow into an additionally provided wire so that a magnetic field is applied thereto. Thus, the two magnetic layers forming each element are controlled to be parallel or anti-parallel to each other, so that “1” or “0” is recorded. Reading is performed by utilizing the GMR and TMR effects.
For an MRAM, the use of the TMR effect results in lower power consumption than the use of the GMR effect. Therefore, the use of the TMR element has been mainly studied. In an MRAM using a TMR element, the MR ratio of change is as large as 20% or more at room temperature, and the resistance at the tunnel junction is large. Therefore, a larger output voltage can be obtained. On the other hand, in the MRAM using such a TMR element, spin reversal is not required to be performed upon reading, so that reading is possible with the less current. For this reason, the MRAM using the TMR element has been expected as a low power consumption type nonvolatile semiconductor memory device capable of high-speed writing/reading.
As for the write operation of the MRAM, it is desired that the magnetic characteristics of the ferromagnetic layers in the TMR element are controlled. Specifically, there are demands for a technology of controlling the relative magnetization directions of two ferromagnetic layers interposing a non-magnetic layer therebetween to be parallel/anti-parallel, and a technology of making the magnetization reversal of one magnetic layer in a desired cell with reliability and efficiency. The technologies of controlling the relative magnetization directions of two ferromagnetic layers interposing a non-magnetic layer therebetween to be uniformly parallel/anti-parallel within the film plane by using two crossing wires have been shown in, for example, patent documents 1, 3, 4, and (Japanese Unexamined Patent Publication No. Hei 11 (1999)-273337, Japanese Unexamined Patent Publication No. 2000-353791, U.S. Pat. No. 6,005,800, and Japanese Unexamined Patent Publication No. 2005-310971).
In an MRAM, when cell miniaturization is performed for higher integration, the reversing magnetic field increases due to the demagnetizing field depending upon the size in the direction of the film plane of the magnetic layer. Thus, a large magnetic field is required for writing, and the power consumption also increases. Therefore, as shown in the patent documents 2, 5, 6, and (Japanese Unexamined Patent Publication No. 2002-280637, Japanese Unexamined Patent Publication No. 2004-296858, U.S. Pat. No. 6,570,783, and Japanese Unexamined Patent Publication No. 2005-310971), there have been proposed technologies wherein the shape of the ferromagnetic layer is optimized thereby to facilitate magnetization reversal.
When miniaturization of a magnetic memory element is carried out with higher integration for an MRAM, a larger magnetic field is required for writing due to the effect of the demagnetizing field. Therefore, the effect of the magnetic field exerted on the periphery of the selected magnetic memory element becomes large, and erroneous magnetization reversal becomes pronounced. In order to cope with it, there has been proposed in, for example, the patent document (Japanese Unexamined Patent Publication No. 2000-353791), that a wire covered with a material of high magnetic permeability as in Permalloy is formed and a TMR element is caused to concentrate the magnetic field thereon.